This invention relates in general to imaging, and more specifically, to a novel, one-step imaging system. Various methods are known for forming visible images in response to a light and shadow image pattern. In many of the common methods the appearance of a light sensitive chemical composition is changed by the action of the light upon the composition. For example, photography and blueprinting are photochemical methods. Other methods are known wherein light is used to alter the hardness, tackiness, solvent resistance, or ink receptivity of various suitable materials.
In recent years, other methods which make use of the electrical properties of photosensitive or photoconductive materials, as distinguished from the chemical properties of imaging compositions, have come into widespread use. For example, a layer of an electrically photosensitive material may be electrically charged and exposed to a pattern of light or other activating electromagnetic radiation, and the resultant electrical pattern, sometimes called an electrical latent image, may be used to control the selective attraction or repulsion of some form of electroscopic marking material to or from the surface of the photosensitive material. In still other systems, electrical conductivity patterns or electrical latent images may be used to control electro-chemical reactions or to create geometrical changes, i.e. deformations, at the surface of imaging compositions. Still other imaging methods have been developed which comprise exposing a layer of a semiconductor material to an imagewise pattern of activating electromagnetic radiation thereby producing a latent image in the semiconductive layer.
There has also recently been developed a migration imaging system capable of producing high quality images of high density, continuous tone, and high resolution. This system is described and claimed in copending applications Ser. No. 837,780, now U.S. Pat. No. 3,975,195, and Ser. No. 837,591, now U.S. Pat. No. 4,013,462, both filed June 30, 1969. In a typical embodiment of this imaging system an imaging member comprising a substrate, a layer of softenable material and electrically photosensitive marking material is latently imaged by electrically charging the member and exposing the charged member to a pattern of activating electromagnetic radiation, such as light. Where the photosensitive migration marking material was originally in the form of a fracturable layer at the upper surface of the softenable layer, particles of the migration marking material in the exposed areas of the imaging member migrate toward the substrate when the member is developed by decreasing the resistance of the softenable layer to migration of the marking material towards said substrate.
There are various other systems for forming such images, wherein non-photosensitive or photosensitively inert, marking materials are arranged in fracturable layers or dispersed throughout the softenable layer in a binder configuration, as described in the aforementioned copending applications which also disclose a variety of methods which may be used to form latent images upon such migration imaging members.
Various means for developing the latent images in the novel migration imaging system may be used. These development methods include solvent wash-away, solvent vapor softening, heat softening, and combinations of these methods, as well as any other method which changes the resistance of the softenable material to the migration of particulate marking material through said softenable layer to allow imagewise migration of the particles toward the substrate. In the solvent wash-away development method, the migration marking material migrates in imagewise configuration toward the substrate through the softenable layer as it is softened and dissolved, leaving an image of migration particles corresponding to the desired image pattern on the substrate, with the material of the softenable layer substantially completely washed away. In the heat or vapor softening development modes, the softenable layer is softened or its viscosity is decreased, to allow imagewise migration of marking material toward the substrate and the developed imaged member generally comprises the substrate having migrated marking particles near the softenable layer-substrate interface, with the softenable layer and unmigrated marking particles intact on the substrate in substantially their original condition.
In one system, as described in copending application Ser. No. 71,781, filed Sept. 14, 1970, a migration developed image is at least in part imagewise transparentized by selectively agglomerating the marking material in either the image or background areas of the imaged member.
All of the above imaging systems typically require a development step or steps to bring the latently imaged member or imaging composition to a developed imaged form, i.e. a form wherein the image is typically visible to the human eye. In the various systems described above, such development steps may variously require the use of electrical, chemical, or other means to accomplish the desired result. The present invention relates to a new and advantageous system for instantaneously imaging a migration-type imaging member without necessitating any specific additional development steps to achieve a visible image.